The present invention relates to fluids useful for subterranean operations, and more particularly, to treatment fluids comprising an environmentally friendly delayed crosslinking complex, and methods of use employing such treatment fluids to treat subterranean formations.
Treatment fluids used in subterranean formations or “subterranean treatment fluids” may be any number of fluids (gaseous or liquid) or mixtures of fluids and solids (e.g., solid suspensions, mixtures and emulsions of liquids, gases and solids) used in subterranean operations. As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid.
In some embodiments of the present invention, it is desirable to viscosify subterranean treatment fluids. Subterranean treatment fluids that may benefit from being viscosified include, but are not limited to, fracturing fluids, drilling fluids, diverting fluids, and gravel packing fluids. Increasing the viscosity of subterranean treatment fluids may be important for a number of reasons.
For example, an increase in a subterranean treatment fluid's viscosity can be important for transferring hydraulic pressure to divert treatment fluids to another part of a formation or for preventing undesired leak-off of fluids into a formation from the buildup of filter cakes. Drilling fluids are typically viscosified as drill cuttings will settle to the bottom of a wellbore if the viscosity is too low. An increase in a subterranean treatment fluid's viscosity may also useful in completion and stimulation operations as subterranean viscosified treatment fluids are typically used to carry particulates to specified locations in a subterranean formation for various purposes. For example, fracturing fluids typically require a sufficiently high viscosity in order to retain proppant particulates in suspension or at least to reduce the tendency of the proppant particulates to settle out of the fracturing fluid as the fracturing fluid flows along the created fracture.
The viscosified treatment fluids used in subterranean operations are oftentimes aqueous-based fluids comprising viscosifying agents. These viscosifying agents are typically polysaccharides which, when hydrated and at sufficient concentration, are capable of forming a viscous solution, often referred to as a gelled fluid. A number of polysaccharides may be used to help viscosify a treatment fluid for use in subterranean operations. These viscosifying agents may be crosslinked through an applicable crosslinking reaction comprising a crosslinking agent. Conventional crosslinking agents usually comprise a metal complex (e.g., aluminum sulfate) or other compound that interacts with at least two polymer molecules to form a “crosslink” between them. As used herein, the term “viscosified treatment fluids” does not imply any particular degree of crosslinking. In other words, a viscosified treatment fluid may have some degree of crosslinking or complete crosslinking.
However, the use of these crosslinking agents may give rise to other problems. For example, conventional crosslinking agents typically yield highly viscous fluids within a very short period of time, often seconds, which can lead to increased friction and reduced pumping rates for treatment fluids. In general, more viscous fluids require more power to pump, which translates to higher costs. Thus, these treatment fluid systems are often limited in their use to shallower, vertical wells. There are also some associated dangers and risks that arise from high friction pressures caused by highly viscous fluids.
Moreover, while some potential delayed crosslinking agents and methods have been identified, many of these are not environmentally friendly and in some embodiments of the present invention, non-compliant with current environmental regulations, especially those that may be in more stringent geographic areas such as the North Sea.